Resistance device



Dec. 25, 1945.

G. L. PEARSON 2,391,506

RES ISTANCE DEVICE Filed March 19, 1942 /NVE/v Tof? By G. L .PEARSON Maw 6.1M

ATTORNEY Patented Dec. 25, 1945 oir @TENT assiste assistance nevica Gerald El. Pearson, Millington, N. nll., assigner to Bell Telephone Laboratories, incorporated, New York, N. lll., a corporation oi New Yori:

appears in this specification or the appended claims, it is intended to designate a resistor having" the foregoing characteristics. Since most of the known materials exhibiting thermistor char'- acteristics and at the same time having sufficient conductivity to render them useful as circuit elements, comprise the semiconductors having high negative resistance-temperature coeicients, eri-i emplary descriptions and explanations in this specification may be made with reference to such materials. It should he understood, however, that such electrically conducting materials as may have a relatively high positive resistancetemperature coefficient, are not thereby excluded from the invention described and claimed.

It has been found that a thermistor may be made to exhibit a negative resistance characteristic. For example, the static voltage-current characteristic curve oi a negative resistancetemperature coedicient resistor rises to a voltage maximum and then falls oi. rlhis declining voltage-current curve is an indication of the negative resistance characteristic. If a sufficient direct current voltage is applied to such a thermister to cias it beyond the voltage maximum point, the device will react to an applied alternating current as ii its resistance were negative, provided the frequency of the alternating current is not too high. thermistor so used may oe made to oscillate. The frequency of oscillation depends upon the heating and cooling ability of the thermistor, i. e., its thermal inertia. .if the device is constructed to have low thermal inertia,

it can. les to oscillate at relatively high re= dueneies.

it is an object of this invention to construct a 'thermistor having low thermal inertia.

A feature of this invention resides in a resistor device constructed to present a very small volume of thermistor material to the applied'current.

Other and further objects and features of the invention will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which: Fig. 1 is an elevational view with parts broken away of one device illustrative of the invention;

Fig. 2 is plan view also with parts broken away of the device of Fig. 1;

Fig. 3 is an enlarged section of a portion oi' the device taken on the line S-i ci 2; and

Fig. i is a :further enlargement of the Contact portion of the device.

rlhe thermistor device it is secured in an envef lope ii by means of a plurality of electrically conductive supports i2, i3, ld and i5. The supm ports, which may be of a suitable alloy wire, may he sealed the .press of the envelope il, which may be of glass. Relative movement between the supports within the envelope -may be inhibited by means of a member it which may be a glass bead fused around said supports.

This device ill; the details of which may be better seen in Figs. 3 and fl, may comprise a pair of iiat spring members 2li and 2li held in spaced parallel relation by 'fastening means 22 and 23 and spacers Ell and 25. The fastening means 22 and 23 may be bolts and nuts as illustrated.. The spacers 2d and 25 are of insulating material, preferably or" a slightly compressible material, such as mica. The springs E@ and 2l may be or clock-spring steel. The fastening means 22 and 23 may be in electrical connection with one of the springs, for example, E@ as illustrated. The other spring 2i may be insulated from the bolts by a member 26 which may also be of mica or other suitable insulating material.

Near one end of springs and 2l and secured to adjacent surfaces thereof are two resistor bodies ill and (See Fig. d.) The bodies 2l and 2s may comprise short lengths of metal wire having a very thin coating of high resistancete'mperature coefficient material thereon. The vires may he of tantalum, tungsten or like metal and the coating may be of boron. a mixture of boron and silicon which may for convenience of expression be designated as horen-silicon, or other semiconductive material having a suitable .resist--l ance-temperature coefficient. The resistor bodies and may he secured to the springs 2t and ii i, respe ely, by weide or other suitable means.

The resistor bodies and are urged toward each other by means of the springs 3i) and 2i, and a small filament tti is interposed between them. The filament which may be of tungsten or tantalum, may be conveniently supported by sandwiching it between the insulating spacers 2G and The assembly just described is as previously indicated supported within the envelope il by supports i2, i3, ifi and i5.

The support i2 may be welded to the tip of bolt V22E with a bent-over end portion thereof resting against the wall of envelope Il as may be best seen in Fig. 2. The support I3 is secured, as by welding, to' the lament 30, and support I4 may be secured to the inner end of spring 2I also by welding. YThe support; I5 may be secured to the tip of bolt 23 with a bent-over projection resting against the wall of the envelope II as with support I2. The bent-over portions of supports I2 and I5 extend, respectively, in opposite directions to act as cooperating props or braces against the envelope walls. The supports I2, I3 and I4 are extended to the exterior of envelope I I since they serve also as electrical connectors. makes connection to spring 20 by way `oi the bolt v22. The supports I3 and I4, as previously indicated, are connected directly to lament 30 and spring 2|, respectively. The disc 3| which is employed as a support for the getter used in evacuation of the envelope may be secured to auxiliary support 32 which is in turn secured, as by weld- I ing, to support Ill.

yfaces. By employing relatively hard 'materials for the contact surfaces the requisite mechanical stability may be obtained with minimum deformation. In a device so constituted proper contact conditions will be maintained under rather severe conditions of shock and vibration.

The thermal and thus the resistance characteristics of the device may be controlled to some extent by means of the yatmosphere surrounding the thermistor. For example, the envelope Il may be evacuated to a relatively low pressure or may be Iilled with a gas, such as helium, at a pressure that is substantiallyv atmospheric. If a gas is employed, it should be one that will not react unfavorably with the elements of the device, particularly the thermistor bodies.

The use oi two thermistor bodies, such as 21 and 28 renders the device more versatile than one having only a single thermistor body. Each of the bodies may be, for example, of different size and of dierent material` or either. Diierent materials may be employed to give the bodies leach a diierent resistivity with approximately the same resistance-temperature coeilicient, or the coeiicients may also be differed by use of suitable materials. For example, by making one thermistor material of boron and the other of a boron-siliconmixture, the contact to theI boron may have a resistivity in the order of six times that to the boron-silicon. A device having thermistor bodies of the same dimensions and material may iind particular use where it is desired to have two like, relatively high speed Support I2 made to act sorxewhat in the manner of a grid in a vacuuntu Besides being capable of oscillation, a device constructed in accordance with this invention, may under suitable conditions be made to act as an amplifier, modulator or other controllable impedance means. l

Although the invention has been disclosed by means of a particular illustrative embodiment thereof, it is to be understood as not limited thereby but by the scope of the appended claims only.

What is claimed is:

1. A resistor device comprising three electrically conducting bodies, means for Vpressing two of said bodies into contact with opposite sides of the third, said two bodies each including at the point of contact a relatively thin, hard layer of high resistance-temperature coeiiicient resistor material, said three bodies being relatively shaped and oriented to provide substantially point contact therebetween, the pressure between said bodies being suflicient to maintain them in mechanically stable contact with minimum deformation thereof at the points of contact,vand means for connecting each body to an electric circuit.

' 2'. A resistor device comprising three conductive bodies, and means for pressing two of said bodies into lcontact with opposite sides of the third,v said two bodies including at the point .of

contact a relatively thin layer of boron, the thirdl a small boron surfaced bodyat the free end oi one spring and a small boron-silicon surfaced body at the free end of the other spring, and a metallic lament secured in said insulating ma terial between said springs and extending .botween said bodies, which areurged into contact with opposite sides of said lament by` said springs, the mating contact surfaces of the bodies and filaments being convex to assure substantially point contact therebetween.

.4. A resistor device comprising two substantially parallel springs of conductive material separated by insulating material, two small boron surfaced bodies each secured to adjacent portions of each of said springs, and a metallic lament secured in said'insulating material between said springs and extending between said bodies. which are urgedinto contact with opposite sides of said iilament by said springs, the mating contact surfaces of the bodies and filament being convex to assure substantially point contact therebetween.

5. A resistor device comprising two substantially parallel cantilever springs of conductive material separated adjacent one end by superposed sheets of relatively resilient insulating material, two small bodies each surfaced with a thin layer of high resistance-temperature coeicient material, secured in opposing relation, one at the free end of each spring, and a metallic filament secured between said insulating layers and extending between said bodies, said springs urging said bodies against opposite surfaces of said lament, the bodies and lament having convex surfaces relatively arranged to provide substantially point contacts therebetween. A

6.1A resistor device comprising a conductive member pressed between two bodies each having a semiconductive surface, said member and bodies being shaped and relatively oriented to provide substantially point contact therebetween, the materials forming each of said semiconductive surfaces having relatively high resistance-temperature coe'icients each of different absolute value. a f

7. A resistor device comprising a conductive member pressed between two bodies each having a semiconductive surface, said member and bodies being shaped and relatively oriented'to provide substantially point contact therebetween, the materials of said semiconductive surfaces each having a relatively different value of resistivity.

8. A resistor device comprising three conducting bodies, and means for pressing two of said bodies into contact with opposite sides of the third, said two bodies each including at the point of contact a relatively thin, hard layer of high resistance-temperature coefficient resistor material, said third body being of a relatively hard 9. A resistor device comprising an envelope, va

plurality of electrically conductive supports secured through one wall of said envelope, two bodies each having a thin lm of high resistancetemperature coefficient material thereon, resilient means for urging said bodies toward one another, insulating means for maintaining portions of said resilient means in spaced, substantially parallel relation, and a metallic lament secured through said insulating means and extending between said bodies, whereby said bodies are in substantially point contact with opposite sides of said filament, said conductive supports maintaining the assembly in spaced relation to the walls of said envelope and providing electrical connection to said bodies and iilament. y

GERALD L. PEARSON. 

